Photo-electric cell



July 30, 1929. L. DE FOREST PHOTO ELECXTRICy CELL Filed Jan. v29, 1927 same reference numerals will be used wheng Patented July d, l'929.

LEE DE FOREST, 0F NEW YORK, N. Y., ASSIGNOR,IBY MESNE ASSIGNMENTS, TO'GEN- ERAL TALKING PICTURES CORPORATION', A CORPORATION 0F DELAWARE.

PHoTo-ELEc'rRrc CELL.

Application filed January 29,

This invention relates to improvements in photo electricrcells and methods of mounting and using the same.' f

One of the objects of this invention is the novel construction of a photo electric cell to' permit location ofAthe active elements thereof close to the walls of the envelope.

A still further object of this invention is an improved photo electric cell construction Jfor use in connection with talking motion pictures,- with the parts so arranged, that the electrodes of the cellmay be located in prox- :imity to the li ht slit.

-A further yo ject of this invention is the construction of a 'photoelectric cell adapted to give improved quality of reproduction of sound. A still further object of this invention is to provide an improved phonofilm attachment including the combination with ra slit plate and backing plate, of a novel form of photol electric cell which permits the lcation of the electrodes close to the light slit.

These and several other objects are success- 'fully secured by means of this invention.

This invention resides substantially in the combination,construction, arrangement and relative location of parts, as will appear from n the following disclosure. l y

Referring to the drawings in which the possible to indicate the same or similar parts, Fig. 1 is a top plan view of my improved photo electric cell construction. a

Fig. 19L is a side elevational view of the cell.

Fig. 2 is a more or less diagrammatic view dwith .some parts in cross section showing the association of the photo electric cell with the light slit and ihn. The cross sectional view is taken on the line 2-2 of Fig. 3, and

Fig. 3 is a side elevational viewof a photo electric cell of my novel construction associated with the split plate and backing plate. In phonolm work, in reproducing sound from a phonographic record on a celluloid film, I have found it advantageous to locate the photo electric cell as near as possibleto the film sound record, sothat the path of light from the sound record to the sensitive element of the hoto electric cell` shallcb'e as short as possi le. I have also found that by locating the sensitive surface of the photo v electric cell close to the iilm I- gain'in ein? ciency by reducin the loss in the light beam and `by centering t e light image linas small a 1927. Serial No. 164,583.

space as possible upon the sensitive mirror surface of the photo electric cell.

I further find by so doing I greatly increase the apparent sensitivity of the ceLl and enhance the over-all efficiency of the light. and

photo electric cell combination. As a resultl ,Referring to Fig.'1, there is shown a photo I electric cell comprising a suitable envelope 1, made, for instance of glass, quarts, and the like. Within the .envelope is an electrode made up of a wire loop 2 having a lead in wire 6. At 3 is shown the sensitive mirror surface electrode 3, which has the lead in wire 5. .At 4 is shown the tip `at which the envelope is sealed oli' after 1t has been cleaned of gases, after the introduction of a suitable gas and subsequent exhaustionthereof. The A i particular vform of the envelope is clearly 'shown in Fig. 1, and is lenticularl in shape; By properly dimensioning this vessel, it isl possible -to bring the electrodes up very close to the front`wall or window vof the vessel, so that 'when the cell is placed very close to the film` a light path of ,minimum length is secured.

In actual construction, it ishighly advantageous'to make this cell "very'small and the actual 4form of cell as I use it is somewhat smaller than the actual cell shown in Figures 1 and 1?. The sensitive mirror of this cell is secured by deposition on a circularvmetal plate. This comprisesthe cathode` of the' cell, while the wire .loop is the ande. This arsmall lenticular and shallow unit form of photo electric cell, which can be directly introduced into the tubular support mounted 'rangement as described and shown gives me a l los , record has been made.

through the condensing lenses 8, so as to be ,A

with the slit plate 9, a vguide for the moving film 12 on which the photographic sound Mounted on the backing plate is a tubular member 11 within which 1s mounted the improved form of phot'o electric cell devised'by me. It may benoted that thedimensions of the cell as given in Figure 2, more nearly approximate the actual Al previous forms of photo electricA cellshave usually been in sphericall form, of one or two inches in diameter, or of a cylindrical form, both of which are ill adapted from a practical view-` point to be permanently located close to the film.

' In my copending patent application, Ser.

No. 121,67 9, filed July 10, 1926, I have shown and described a form of film gate construction for phonofilm work, wherein the photo electric' cell is located at a distance of at least two or more inches from the film. In this and similar practical arrangements of the .iilm

' gate and backing` plate it has been necessary or highly advantageous to remove the backing plate from time to time in order to readily thread the film into the device or to clean 0E the dirt and cake emulsion, which gradually accumulates thereon.

This arrangement rendere-d it impossible to place the heretofore used types of photo electric cells close to the film, and thereforeim possible to take advantage of the fact, which I have discovered here, of locating the photo electric cell close to the slit and film.

After the cell has been located Within the tubular member 11 in its proper` place it may be permanently secured therein by pouring around it molded paraliine or soft plaster of Paris. Thereaften'thelcell, the supporting tube, and the block are integral. By this arrangement, I find a greatfreduction or entire i elimination of the microphonic noises, which are frequently setup in the operation of the phonofilm apparatus in connection with motion picture projectures due to mechanical vibrations of the photo electric `cell in its hol-der, relativeto the beam of llight Which is passing through the film. In view of the ex- 1,722,2so 'h tremely small dimensions, of thecelldevised by me the anode ring being supported by a short piece of wire within the cell has very little tendency to vibrate with consequent diminution of the microphonic noises, which the vibration of the anode with respect to the cathode or with the beam of light falling on the cathode would. produce. Y

In order to provide means for readily connecting and disconnecting the cell, the leads 5 and 6, shielded, if desired, may be connected to terminal blocks mounted permanently at 14 and 15, respectively. These blocksor contacts are so arranged, that when the backing plate is slipped into place in the reproducing mechanism, contact is made between these blocks and suitable jacks 16 and 17, which are connected by the leads 18 and 19, respectively, to theaudion amplifier usually used in said arrangements. At 21 are shown the usual springs which areused in such devices for bracing vthe backing plate against the film. l

-As a practical consideration, I may point.

out that I am able to permanently locate the sensitive mirror surface of the photo electric cell as close as one-fourth to one-half inch to the film, thus achieving the many advantages which I have pointed out above.

I am aware thatmany changes in the details of construction and relative arrangement of parts will readily suggest themselves to those skilled in this art, and Ido not, therefore, desire to be limited to the.l exact constructions shown for the purpose of illustrating my invention, but rather to the scope of my invention as defined in the appended claims.

What I seek to secure by United States.

Letters Patent is as follows: I claim:

A phonofilm attachment comprising a slit In 'testimony whereof I have hereunto Set my7hand on-this 25th day of January, A. D. 192

DE FOREST. 

